Enhanced IQ mismatch correction function generator

ABSTRACT

An IQ mismatch correction function generator configured to generate an enhanced IQ mismatch correction function to improve the compensation for IQ mismatch, and an IQ signal receiver with the IQ mismatch correction function generator, wherein the enhanced IQ mismatch correction function is determined based on an initial IQ mismatch correction function derived from IQ mismatch estimates corresponding to frequency bins where signals are present and error of the initial IQ mismatch correction function by comparing the values of the initial IQ mismatch correction function with IQ mismatch estimates corresponding to a respective bin of the frequency bins.

RELATED APPLICATIONS

This application claims priority to Indian Provisional Application No.201841041535, filed Nov. 2, 2018, and U.S. Provisional Application No.62/786,727, filed Dec. 31, 2018, which are hereby incorporated byreference.

BACKGROUND

In a quadrature signal system, baseband signal may comprise two-realsignals: in-phase (I) and quadrature-phase (Q) signals. These I and Qbaseband signals are multiplied with cosine and sine waves of a RFtransmitter and combined to generate a RF passband signal (IQ RFsignals). Ideally, the cosine and sine waves of the RF transmitter havethe same amplitude and differ in phase by 90 degrees, thereby making theIQ RF signals a pair of quadrature signals. Zero-IF receiver employshomodyne or direct down conversion method to receive this pair ofquadrature signals. During the direct down conversion, the passbandsignal is mixed with the in-phase and quadrature-phase components of alocal oscillator signal to generate IQ baseband signals for furtherbaseband processing.

While receiving the IQ RF signals, it is important to maintain theamplitude and phase relationship between the I and Q signals to ensurean accurate signal reception. It is also important to maintain the samegain and the 90 degree phase relationship between the in-phase andquadrature-phase components of the local oscillator to prevent a gain orphase skew between the I and Q signals. In reality, however, errors suchas an IQ gain/phase imbalance existing in a zero-IF receiver impairs theamplitude and phase relationship between the IQ RF signals. Such IQgain/phase imbalances are due to mismatches in the gain and phasebetween the components of the local oscillator, and the mismatches inthe analog filters and analog-digital converters (ADC) between the I andQ paths.

A correction is attempted to compensate for impairments caused by IQmismatch by estimating the IQ mismatch. The zero-IF receiver may, inturn, compensate for skews on the pair of quadrature signals bycorrecting the quadrature signals based on the IQ mismatch estimates.

SUMMARY

An aspect of the present invention provides an IQ mismatch correctionfunction generator configured to generate an enhanced IQ mismatchcorrection function to improve the compensation for IQ mismatch, and anIQ signal receiver with the IQ mismatch correction function generator.

Yet another aspect of the present invention to improve the compensationof IQ mismatch provides an initial IQ mismatch correction functiongenerator configured to generate an initial IQ mismatch correctionfunction based on IQ estimates at least one frequency bin, an errormitigation logic configured to determine an error of the initialmismatch correction function, and enhanced IQ mismatch correctionfunction generator configured to generate an enhanced IQ mismatchcorrection function based on the initial IQ mismatch correction functionand the error determined by the error mitigation logic to enhance theaccuracy of IQ mismatch estimates.

Yet another aspect of the present invention to improve the compensationfor IQ mismatch provides an IQ mismatch correction function generatorconfigured to generate an initial IQ mismatch correction function and anenhanced IQ mismatch correction function, and a feedback loop configuredto determine a difference between the values of the initial IQ mismatchcorrection function corresponding to at least one frequency bin and IQmismatch estimates corresponding to a respective bin of the at least onefrequency bin, and output the difference as error of the initial IQmismatch correction function to the IQ mismatch correction functiongenerator to generate the enhanced IQ mismatch correction function.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 illustrates a block diagram of a prior art zero-IF receiver;

FIG. 2 illustrates a signal spectrum of baseband signal and image signalof the baseband signal due to IQ mismatch;

FIG. 3 illustrates a block diagram of a zero-IF receiver according to anaspect of the present invention;

FIG. 4 illustrates a block diagram of a correction function moduleaccording to an aspect of the present invention;

FIGS. 5A-5C illustrate graphs of initial IQ mismatch correction functionand enhanced IQ mismatch correction function according to an aspect ofthe present invention across plurality of frequency bins;

FIG. 6 illustrates a block diagram of a correction function moduleaccording to yet another aspect of the present invention;

FIG. 7 illustrates a block diagram of an error mitigation logicaccording to an aspect of the present invention;

FIG. 8 illustrates a block diagram of a correction function moduleaccording to yet another aspect of the present invention; and

FIG. 9 illustrates the cumulative distribution functions of errorsexisting in IQ mismatch correction function generated according to anaspect of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to certainexamples of the present invention. These examples are described withsufficient detail to enable those skilled in the art to practice them.It is to be understood that other examples may be employed and thatvarious structural, logical, and electrical changes may be made.Moreover, while specific examples are described in connection with azero-IF receiver, it should be understood that features described hereinare generally applicable to zero-IF transmitter and other types ofsystems like low-IF transmitters, receivers, and transceivers,electronic parts, circuits, or other types of transmitters and receiverswith changes well known to those skilled in the art.

In this description, the term “couple” or “couples” means either anindirect or direct wired or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections. For another instance, when a first device is coupled to asecond device, the first and second device may be coupled through acapacitor. The recitation “based on” means “based at least in part on.”Therefore, if X is based on Y, X may be a function of Y and any numberof other factors.

FIG. 1 illustrates a block diagram of a zero-IF receiver according to anexample of prior art. The prior art zero-IF receiver of FIG. 1 comprisesamplifier 110 amplifying the received quadrature passband signals, mixer115 down-converting the amplified quadrature passband signals within-phase and quadrature-phase components of a local oscillator signal,and filter 120 filtering signals within the frequency range of interest.

The zero-IF receiver of FIG. 1 further comprises analog digitalconvertor 125 to convert the filtered signal from filter 120 intodigital signals, an optional decimation filter 130 reducing the rate ofthe digital signals, IQ imbalance estimation module 135 estimating theIQ imbalance based on the down-converted digital signals, and IQmismatch correction module 140 correcting the digital signals outputfrom decimation filter 130 to compensate for IQ imbalance estimated inthe digital signals.

FIG. 2 illustrates a frequency spectrum of baseband signal and imagesignal of the baseband signal due to IQ mismatch. In the example of FIG.2, signals on the right pane of frequency spectrum, positive frequencysignals, reflect the original signal X_(orig)(f) transmitted from azero-IF transmitter. In an ideal zero-IF transmitter and zero-IFreceiver without an IQ mismatch, only the original signal X_(orig)(f)should be observed when the zero-IF receiver processes the quadraturepassband signals to baseband signals. Because of IQ mismatch, however,the output signal includes an image signal, in the example of FIG. 2,H(f)X_(orig)*(−f) of negative frequency.

In FIG. 2, H(f) is an IQ mismatch function, which may be estimated basedon an IQ mismatch estimation algorithm. The IQ mismatch function H(f)may be used by a zero-IF receiver to compensate a signal skew due to IQmismatch.

FIG. 3 illustrates a block diagram of a zero-IF receiver according to anaspect of the present invention. The zero-IF receiver of FIG. 3comprises amplifier 310 configured to amplify the passband quadraturesignals received by the zero-IF receiver, mixer 320 configured to mixthe in-phase and quadrature-phase components of a local oscillatorsignal with the amplified passband signals to generate basebandquadrature signals, and filter 330 configured to filter the basebandquadrature signals. In the example of FIG. 3, amplifier 310 includes lownoise amplifier 311 configured to amplify the received signal anddigital step amplifier 312 configured to be gain adjustable. Filter 330of FIG. 3 may be a lowpass filter configured to low pass signals undercertain frequency while filtering noise and interferers from the mixedquadrature signals.

Quadrature signals output from filter 330 is converted into digitalsignals by analog digital convertor 340. The digital quadrature signalsmay further be decimated into an acceptable sampling rate preferable fora system receiving the passband quadrature signals by decimation filter350.

IQ imbalance estimation module 360 estimates H_(valid), which is IQimbalance or mismatch corresponding to frequency bins where signals arepresent, i.e., valid bins. For instance, where 10 MHz and 100 MHzbaseband signals were transmitted, IQ imbalance estimation module 360estimates IQ imbalance corresponding to 10 MHz frequency bin and 100 MHzfrequency bin. The terms imbalance and mismatch are used interchangeablyin this specification.

Correction function module 370 generates a correction function providedto IQ mismatch correction filter 380 to compensate digital quadraturesignals output from decimation filter 350 for IQ mismatch. Thecorrection function(s) generated by correction function module 370serves as correction filter coefficients of IQ mismatch correctionfilter 380. According to an aspect of the present invention, correctionfunction module 370 generates an initial IQ mismatch correction function(h_(corr)), and based on the errors of the initial correction function,may further generate an enhanced IQ mismatch correction function(g_(corr)). Either the initial IQ mismatch correction function or theenhanced IQ mismatch correction function serves as correction filtercoefficients of IQ mismatch correction filter 380.

An initial IQ mismatch correction filter coefficients of IQ mismatchcorrection filter 380, which are values of initial IQ mismatchcorrection function h_(corr) generated by correction function module370, is obtained based on the estimates of H(f) at the valid bins,H_(valid). As noted above, H_(valid) is provided by IQ imbalanceestimation module 360. Correction function module 370 interpolatesH_(valid) across all frequency bins and then inverse fast fouriertransforms (IFFT) the interpolated H_(valid), H_(int), to its timedomain equivalents, h_(int). The time domain equivalents of theinterpolated IQ estimates at the valid bins are, in turn, truncated toeliminate coefficients that are beyond an assigned filter length. Thetruncated time domain equivalents of the interpolated H_(valid) make upthe initial IQ correction function, h_(corr), generated by correctionfunction module 370.

The process of truncation to generate the initial IQ mismatch correctionfunction, h_(corr), may introduce additional errors while correcting IQmismatch. To reduce the additional IQ mismatch caused by truncation, anaspect of the present invention obtains the error between the estimatesof H(f) at the valid bins, H_(valid), and fast fourier transform (FFT)version of the initial IQ mismatch correction function h_(corr),H_(corr), at the valid bins. This error is then used to generate anenhanced IQ mismatch correction function, g_(corr), and update thefilter coefficients to be used for IQ mismatch correction. This processcan be iterated multiple times. These aspects of the present inventionmay be implemented using various architectures. FIGS. 4-8 illustrateexamples of these various architectures.

FIG. 4 illustrates a block diagram of correction function module 370 ofFIG. 3 according to an aspect of the present invention. Correctionfunction module 370 of FIG. 4 comprises initial IQ mismatch correctionfunction generator 410, error mitigation logic 430, and enhanced IQmismatch correction function generator 450.

Initial IQ mismatch correction function generator 410 is configured togenerate an initial IQ mismatch correction function h_(corr) for IQmismatch correction filter 380 based on the estimates of H(f) at validbins, H_(valid). As noted above, the initial IQ mismatch correctionfunction h_(corr) generated by initial IQ mismatch correction functiongenerator 410 serves as the initial IQ mismatch correction filtercoefficients of IQ mismatch correction filter 380 of FIG. 3. H_(valid)is output from IQ imbalance estimation module 360 of FIG. 3. Valid binsare frequency bins where signals are present. At any point in time,there may be one valid bin, or more than one valid bins. Initial IQmismatch correction function generator 410 generates the initial IQmismatch correction function h_(corr) by first interpolating the IQmismatch estimates H_(valid) by interpolator 411.

Interpolator 411 may employ various interpolation or extrapolationmethods to interpolate the IQ mismatch estimates at valid bins,H_(valid). For example, in FIG. 5, which illustrate graphs of the FFTversions of the initial IQ mismatch correction function, h_(corr), andenhanced IQ mismatch correction function, g_(corr), generated accordingto an aspect of the present invention, interpolator 411 may generate aninterpolated IQ mismatch estimates H_(hint) by linearly interpolatingH_(valid), as shown in graph (a) of FIG. 5.

More specifically, graph (a) of FIG. 5 illustrates IQ mismatch estimatesat three frequency bins f1, f2, and f3, which are H_(valid) provided byIQ imbalance estimation module 360, and interpolated IQ mismatchestimates H_(int), which are output from interpolator 411. In FIG. 5graph (a), interpolator 411 linearly interpolates the IQ mismatchestimates H_(valid) to provide interpolated IQ mismatch estimatesH_(int) across a range of frequency of interest. In the drawings, themismatch estimates are shown as real functions for ease of depictionalthough in reality they may be complex functions.

Interpolated IQ mismatch estimates H_(int) is inverse fast fouriertransformed into its time domain equivalents h_(int) by inverse fastfourier transform logic 412, and truncated to reduce the number of tapsof IQ mismatch correction filter 380 by truncator 413. Output oftruncator 413 is the initial IQ mismatch correction function, h_(corr),generated by initial IQ mismatch correction function generator 410. Fastfourier transform logic 420, which may be employed by and form a part oferror mitigation logic 430, computes fast fourier transform of theinitial IQ mismatch correction function, h_(corr), to generate afrequency domain equivalent of the initial IQ mismatch correctionfunction h_(corr), H_(corr). According to yet another example, fastfourier transform logic 420 may be employed by and form a part ofinitial IQ mismatch correction function generator 410.

As observed in graph (a) of FIG. 5, the frequency domain equivalent ofthe initial IQ mismatch correction function H_(corr) does not follow thepaths of either IQ mismatch estimates H_(valid) or interpolated IQmismatch estimates H_(int). The error, which is indicated on graph (a)by arrows between the frequency domain equivalent of the initial IQmismatch correction function H_(corr) and IQ mismatch estimatesH_(valid), is caused by the truncation function performed by truncator413 to reduce the number of taps.

Error mitigation logic 430 computes the error between the frequencydomain equivalent of the initial IQ mismatch correction functionH_(corr) and IQ mismatch estimates at the valid bins, H_(valid), togenerate error function H_(err), which is illustrated in graph (b) ofFIG. 5. In particular, in the example of FIGS. 4 and 5, error mitigationlogic 430 calculates differences of the frequency domain equivalent ofthe initial IQ mismatch correction function H_(corr) from IQ mismatchestimates H_(valid) at the valid bins, e.g., frequency bins f1, f2, andf3. And based on the differences, error mitigation logic 430 outputserror function H_(err) to enhanced IQ mismatch correction functiongenerator 450.

In the example of FIGS. 4 and 5, error function H_(err) generated byerror mitigation logic 430 estimates errors across the entire frequencyrange of interest, in addition to three errors corresponding to validfrequency bins f1, f2, and f3, by interpolating the three errors asillustrated in graph (b) of FIG. 5. This interpolation may be based onan linear interpolation or any other known interpolation scheme.According to another aspect of the present invention, error function maysimply be the errors corresponding to the frequency bins f1, f2, and f3,and 0s elsewhere with optional scaling on the three errors as well.According to yet another aspect of the present invention, error functionmay be based on a subset of low uncertainty errors as described inrelation to FIG. 7.

Enhanced correction function generator 450 generates a frequency domainenhanced IQ mismatch correction function G_(corr) (expressed as g_(corr)in time domain) based on the frequency domain equivalent of the initialIQ mismatch correction function H_(corr) and error function H_(err). Inthe example of FIG. 4, enhanced IQ correction function generator 450comprises sum logic 451 configured to add error function H_(err) to thefrequency domain equivalent of the initial IQ mismatch correctionfunction H_(corr) to generate an error adjusted initial IQ mismatchcorrection function G_(adj), inverse fast fourier transform logic 452configured to inverse fast fourier transform the output of sum logic 451and generate the time domain equivalent g_(adj) of error adjustedinitial IQ mismatch correction function G_(adj), truncator 453configured to truncate the time domain equivalent of error adjustedinitial IQ mismatch correction function, g_(adj), to reduce a number oftaps of IQ mismatch correction filter 380 and generate enhanced IQmismatch correction function g_(corr) in time domain.

Graph (c) of FIG. 5 illustrates IQ mismatch estimates at valid bins,H_(valid), from IQ imbalance estimation module 360, the frequency domainequivalent of the initial IQ mismatch correction function H_(corr) fromfast fourier transform logic 420, error adjusted initial IQ mismatchcorrection function G_(adj) output from sum logic 451, and the frequencydomain equivalent of the enhanced IQ mismatch correction functiong_(corr) output from truncator 453, G_(corr). As illustrated in graph(c), the difference between frequency domain enhanced IQ mismatchcorrection function G_(corr) and IQ mismatch estimates H_(valid) issignificantly lower than the difference between frequency domain initialIQ mismatch correction function H_(corr) and IQ mismatch estimatesH_(valid).

According to an aspect of the present invention, IQ mismatch correctionmodule may further comprise feedback logic 454 configured to feedbackenhanced IQ mismatch correction function g_(corr) to error mitigationlogic 430, after the fed back time domain enhanced IQ mismatchcorrection function g_(corr) is fast fourier transformed into frequencydomain by fast fourier transform logic 420. FIG. 6 illustrates an IQmismatch correction module including feedback logic 454 according to anaspect of the present invention. When g_(corr) is fed back to fastfourier transform logic 420, error mitigation logic 430 is configured tocompute error function H_(err) based on G_(corr) instead of H_(corr).Enhanced IQ mismatch correction function generator 450 generates thetime domain equivalent g_(adj) error adjusted initial IQ mismatchcorrection function G_(adj) based on the error function H_(err) fromerror mitigation logic 430, wherein the error function H_(err) is basedon G_(corr).

In other words, in the example of FIG. 6, error mitigation logic 430 isfurther configured to determine errors of enhanced IQ correctionfunction G_(corr) by comparing the difference of the values of enhancedIQ correction function G_(corr) corresponding to three frequency binsf1, f2, and f3, from the IQ mismatch estimates H_(valid). Enhanced IQmismatch correction function generator 450 is further configured togenerate a subsequent enhanced IQ mismatch correction function based onthe fed back enhanced IQ mismatch function G_(corr) and the error of thefed back enhanced mismatch correction function G_(corr) by repeating theprocess described in relation to FIGS. 4 and 5. The feedback andgeneration of subsequent enhanced IQ mismatch correction function maycontinue until the error of the last enhanced IQ mismatch correctionfunction is lower than a threshold value. If all errors based on the fedback enhanced mismatch correction function G_(corr) is below athreshold, there is no need to update the IQ mismatch correctionfunction any further, and the current value of the IQ mismatchcorrection function may be used as coefficients of IQ mismatchcorrection filter 380.

FIG. 7 illustrates a block diagram of error mitigation logic 430 of FIG.4 or 6 according to an aspect of the present invention. Error mitigationlogic 430 comprises error computer 431 configured to compute the errorof the frequency domain initial IQ mismatch correction function H_(corr)based on the difference between IQ mismatch estimates at valid bins,H_(valid), and the values of the frequency domain initial IQ mismatchcorrection function H_(corr) (or enhanced IQ mismatch correctionfunction G_(corr) when G_(corr) is fed back by feedback block 454) at arespective bin of the valid bins. The error is shown in FIG. 7 asH_(err, comp). Mathematically, H_(eer, comp) can be expressed as theresult of subtracting H_(corr) or G_(corr) from H_(valid) (i.e.,H_(err, comp)=H_(valid)−H_(corr)(or G_(corr))).

According to another aspect of the present invention, error mitigationlogic 430 may further include options logic 432, which is configured todetermine quality metrics, uncertainty, with each error. The uncertaintyof the error is computed based on the uncertainty of IQ mismatchestimates at valid bins, H_(valid), which is determined by IQ imbalanceestimation module 360 of FIG. 3. In one example, the uncertainty of theerror may be the uncertainty of H_(valid) itself.

Options logic 432, in turn, selects a subset of errors whose uncertaintylevel is less than a threshold times the error value computed by errorcomputer 431, and outputs the selected subset of errors, H_(err, sel).For other bins where uncertainty is larger than a threshold times theerror value, H_(err,sel) is made 0 as there is no need to update thesebins. This is because, when the error times the threshold is below theuncertainty, there is need to improve the corresponding estimate.Enhanced

IQ correction function generator 450 may generate an enhanced IQmismatch function based on selected errors H_(err, sel), instead oferrors calculated by error computer 431, H_(err, comp).

According to an aspect of the present invention, error mitigation logic430 further include error extension logic 433 configured to interpolatethe error values computed by error computer 431 across the entirefrequency range of interest and generate error function H_(err). Forexample, error extension logic 433 may generate error function H_(err)by linearly interpolating the error values computed by error computer431, H_(err, comp), as illustrated in graph (b) of FIG. 5. In anotherexample, error extension logic 433 generates error function H_(err)based on errors computed at the valid bins, H_(err, comp), and 0s forthe remaining frequency bins. Error extension logic 433 may optionallyscale the errors computed at the valid bins, H_(err, comp), whilegenerating error function H_(err) by providing 0s for the remainingfrequency bins. In an example of error mitigation logic 430 including anoptions logic 432, error extension logic 433 generates error functionH_(err) based on a subset of errors selected by options logic 432,H_(err, sel).

FIG. 8 illustrates another example of correction function module 370according to yet another aspect of the present invention. In the exampleof FIG. 8, correction function module 370 comprises IQ mismatchcorrection function generator 810 configured to generate an initial IQmismatch correction function, h_(corr), and enhanced IQ mismatchcorrection function, g_(corr), based on IQ mismatch estimates at validbins, H_(valid), and feedback loop 830 configured to feedback either theinitial IQ mismatch correction function, h_(corr), or the enhanced IQmismatch correction function, g_(corr), to the IQ mismatch correctionfunction generator 810. The IQ mismatch correction function generator810 is further configured to determine the error of the fed back initialIQ mismatch correction function, h_(corr), or enhanced IQ mismatchcorrection function, g_(corr), and generate a subsequent IQ mismatchcorrection function based on the error.

In FIG. 8, the initial IQ mismatch correction function, h_(corr), is anIQ mismatch correction function output from IQ mismatch correctionfunction generator 810 based on IQ mismatch estimates at valid bins,H_(valid). The enhanced IQ mismatch correction function, g_(coor), is aIQ mismatch correction function output from IQ mismatch correctionfunction generator 810, subsequent to the initial IQ mismatch correctionfunction, h_(corr). The enhanced IQ mismatch correction function,g_(corr), is generated based on the fed back initial IQ mismatchcorrection function, h_(corr), and IQ mismatch estimates at valid bins,H_(valid). Depending on the error levels of the enhanced IQ mismatchcorrection function, g_(corr), a subsequent version of the enhanced IQmismatch correction function may be generated based on the fed backenhanced IQ mismatch correction function, g_(corr), and IQ mismatchestimates at valid bins, H_(valid).

The initial IQ mismatch correction function, h_(corr), is generated byIQ mismatch correction function generator 810 according to thefollowing. First, interpolator 811 interpolates IQ estimates at validbins, H_(valid), based on an interpolation or extrapolation method. Inone example, interpolator 811 may interpolate IQ estimates at validbins, H_(valid), pursuant to the interpolation method adopted byinterpolator 411 of FIG. 4. The output of interpolator 811, interpolatedIQ mismatch estimates H_(int), is inverse fast fourier transformed byinverse fast fourier transform logic 812, and truncated to reduce thenumber of taps of IQ mismatch correction filter 380 by truncator 813.The output of truncator 813 based on IQ estimates at valid bins,H_(valid), is the initial IQ mismatch correction function, h_(corr). Thefunctions of inverse fast fourier transform logic 812 and truncator 813are substantially similar to the functions of inverse fast fouriertransform logic 412 and truncator 413 of FIG. 4, respectively.

The initial IQ mismatch correction function, h_(corr), is fed back to IQmismatch correction function 810 via feedback loop 830. In FIG. 8,feedback loop 830 comprises fast fourier transform logic 831 configuredto fast fourier transform the initial correction function, h_(corr), tofrequency domain, H_(corr), and sum logic 832 configured to subtract thefrequency domain initial IQ mismatch correction function H_(corr) fromthe IQ estimates at valid bins, H_(valid). The output of sum logic 832,H_(err), comprises error of the initial IQ mismatch correction function,h_(corr).

IQ mismatch correction function generator 810 comprises convergencedetector 821 configured to determine whether the error of the initial IQmismatch correction function, h_(corr), is within an acceptable range bydetermining whether the initial IQ mismatch correction function,h_(corr), is converged to be within an acceptable range of error from IQestimates at valid bins, H_(valid). Where convergence detector 821determines that the initial IQ mismatch correction function is withinthe acceptable range of error based on the output of sum logic 832,H_(err), the initial IQ mismatch correction function, h_(corr), isprovided as filter coefficients to IQ mismatch correction filter 380 ofFIG. 3.

Conversely, where convergence detector 821 determines that the initialIQ mismatch correction function is not within the acceptable range oferror, IQ mismatch correction function generator 810 generates theenhanced IQ mismatch correction function, g_(corr), according to thefollowing. First, interpolator 811 interpolates the output of sum logic832, H_(err), based on an interpolation or extrapolation method. Theoutput of sum logic 832, H_(err), is the error of the initial IQmismatch correction function, h_(corr), at valid bins. Interpolator 811interpolates the output of sum logic 832, H_(err), across thefrequencies relevant to a receiver. In one example, interpolator 811 mayinterpolate H_(err) by linearly interpolating the error in IQ estimatesat valid bins. In another example, the output of interpolator 811 maysimply be the errors corresponding to the valid bins and 0s elsewherewith optional scaling on the valid bin errors.

Convergence detector 821, according to yet another example of thepresent invention, may select errors from which the enhanced IQ mismatchcorrection function, g_(corr), shall be generated. For example,convergence detector 821 may be further configured to determine qualitymetrics, uncertainty, with each error corresponding to the valid bins.The uncertainty of the error is computed based on the uncertainty of IQmismatch estimates at the valid bins, H_(valid). In one example, theuncertainty of the error may be the uncertainty of H_(valid) itself

Convergence detector 821 selects a subset of errors whose uncertaintylevel is less than a threshold times each values of H_(err), and outputsthe selected subset of errors, as H_(err, sel), to interpolator 811. Forbins where uncertainty is larger than a threshold times thecorresponding error value, the error value is replaced with 0 as thereis no need to update these bins. Interpolator 811, in turn, interpolatesH_(err, sel), to generate error across the relevant frequencies, thenoutput as Hint

Inverse fast fourier transform logic 812 inverse fast fourier transformsthe interpolated H_(int), and truncator 813 truncates the inverse fastfourier transformed H_(int) according to the filter length size of IQmismatch correction filter 380. The initial IQ mismatch correctionfunction, h_(corr), is time delayed via delay logic 823 and output tosum logic 825. Sum logic 825 generates the enhanced IQ mismatchcorrection function, g_(corr), based on the output of truncator 813 andthe time delayed initial IQ mismatch correction function, h_(corr). Inone example, the initial IQ mismatch correction function, h_(corr), istime delayed to be provided to sum logic 825 when truncator 813 outputsthe time domain, interpolated and truncated error. In the example ofFIG. 8, sum logic 825 generates the enhanced IQ mismatch correctionfunction, g_(corr), by adding the time delayed initial IQ mismatchcorrection function, h_(corr), with the time domain, interpolated andtruncated error.

Correction function module 370 may further generate a subsequentenhanced IQ mismatch correction function after the enhanced IQ mismatchcorrection function, g_(corr), is fed back via feedback loop 830. Sumlogic 832 determines the error of enhanced IQ mismatch correctionfunction, g_(corr), by subtracting the values of the enhanced IQmismatch correction function, g_(corr), from the IQ estimates at validbins, H_(valid). Convergence detector 821 compares the error, H_(err),output from sum logic 832 of valid bins with a threshold multiplied bythe uncertainty of the corresponding IQ estimate at each valid bins, ormerely compares the error with a threshold. The comparison may be basedon the absolute value of the error.

Where the error is less than the compared value, there is no need togenerate any subsequent iterations of IQ mismatch correction functionsfor that bin. This implies that that valid bin's estimate has beenconverged. In this case, the H_(err) is made 0 for that the respectivebin. H_(err) for other bins, of which the error is not less than themultiple threshold value or other compared value, retains the errorvalue output from sum logic 853. IQ mismatch correction functiongenerator 810 generates a subsequent version of the enhanced IQ mismatchcorrection function based on the H_(err) calculated from the enhanced IQmismatch correction function, g_(coor).

The process of generating subsequent versions of enhanced IQ mismatchcorrection function is repeated until the errors corresponding to allvalid bins is less than the multipled threshold value. In anotherembodiment, the process is repeated a number of times or for a period oftime.

FIG. 9 illustrates the cumulative distribution functions of errorsexisting in IQ mismatch correction function generated according to anaspect of the present invention. In FIG. 9, estimates are obtained fortwo adjacent bins, where bin selection is a randomized across runs. Asillustrated, an output based on an example of the present inventionimproves its performance significantly, which delivers over 10 dB ofimprovement.

The above description and drawings are only to be consideredillustrative of an example of the present invention which achieves thefeatures and advantages described herein. Modifications are possible inthe described examples, and other examples are possible, within thescope of the claims. Accordingly, the examples of the present inventiondescribed herein is not considered as being limited by the foregoingdescription and drawings.

What is claimed is:
 1. An in-phase and quadrature-phase (IQ) signalreceiver comprising; an IQ imbalance estimation circuit configured toestimate IQ mismatch corresponding to at least one frequency bin basedon a signal received by the IQ signal receiver; a correction functioncircuit coupled to the IQ imbalance estimation circuit and generate atleast one IQ mismatch correction function based on the IQ mismatchestimates of the IQ imbalance estimation circuit; and an IQ mismatchcorrection function circuit coupled to the correction function circuitand compensate the signal received by the IQ signal receiver for IQmismatch based on the IQ mismatch correction function generated by thecorrection function circuit; wherein, the at least one IQ mismatchcorrection function circuit comprises an initial IQ mismatch correctionfunction generated based on the IQ mismatch estimates generated by theIQ imbalance estimation circuit, and an enhanced IQ mismatch correctionfunction generated based on a difference between a value of the initialIQ mismatch correction function corresponding to the at least onefrequency bin and the IQ mismatch estimates corresponding to arespective bin of the at least one frequency bin.
 2. The IQ signalreceiver of claim 1, wherein the at least one frequency bin correspondsto the frequency of the signal received by the IQ signal receiver. 3.The IQ signal receiver of claim 1, wherein the IQ mismatch correctionfunction circuit comprising; an initial IQ mismatch correction functiongenerator configured to generate the initial IQ mismatch correctionfunction; an error mitigation circuit configured to determine an errorof the initial IQ mismatch correction function based on the differencebetween the value of the initial IQ mismatch correction functioncorresponding to the at least one frequency bin and the IQ mismatchestimates corresponding to the respective bin of the at least onefrequency bin; and an enhanced IQ mismatch correction function generatorconfigured to generate the enhanced IQ mismatch correction functionbased on the initial IQ mismatch function and the error of the initialIQ mismatch correction function.
 4. The IQ signal receiver of claim 3,wherein the initial IQ mismatch correction function generator comprises,an interpolator configured to interpolate the IQ mismatch estimatesgenerated by the IQ imbalance estimation circuit; an inverse fastfourier transform circuit configured to inverse fast fourier transformthe interpolated IQ mismatch estimates generated by the interpolator;and a truncator configured to truncate the interpolated and inverse fastfourier transformed IQ mismatch and generate the initial IQ mismatchcorrection function.
 5. The IQ signal receiver of claim 4, wherein theIQ mismatch correction function circuit further comprises a fast fouriertransform circuit configured to fast fourier transform an output fromthe truncator to generate a frequency domain initial IQ mismatchcorrection function, and wherein the error of the initial IQ mismatchcorrection function is determined based on an output of the fast fouriertransform circuit.
 6. The IQ signal receiver of claim 3, wherein theerror mitigation circuit comprises, an error circuit configured tocompute the error of the initial IQ mismatch correction function; and anerror extension circuit configured to generate an error functioncorresponding to a plurality of frequency bins based on the error of theinitial IQ mismatch correction function, wherein the plurality offrequency bins comprises frequency bins of the IQ signal receiver. 7.The IQ signal receiver of claim 6, wherein the error extension circuitis configured to generate the error function by linearly interpolatingthe error of the initial IQ mismatch correction function across theplurality of frequency bins.
 8. The IQ signal receiver of claim 6,wherein the error mitigation circuit further comprises, an optionscircuit configured to select a subset of the error computed by the errorcircuit based on a threshold value; and wherein the error extensioncircuit is configured to generate the error function based on the subsetof error selected by the options circuit.
 9. The IQ signal receiver ofclaim 8, wherein the IQ mismatch estimate of the at least one frequencybin comprises a first IQ mismatch estimate of a first frequency bin anda second IQ mismatch estimate of a second frequency bin; wherein theerror of the initial IQ correction function computed by the errorcircuit comprises a first error corresponding to the first frequency binand a second error corresponding to second frequency bin; and whereinthe options circuit is further configured to select the subset byselecting either or both of the first and second errors by determiningwhether the first and second errors are above the threshold valuemultiplied by a quality metric of the first IQ mismatch estimate and thesecond IQ mismatch estimate, respectively.
 10. The IQ signal receiver ofclaim 3, wherein the enhanced IQ mismatch correction function generatorcomprises, a sum circuit configured to add the error of the initial IQmismatch correction function determined by the error mitigation circuitto the initial IQ mismatch correction function to output an erroradjusted initial IQ mismatch correction function; an inverse fastfourier transform circuit configured to inverse fast fourier transformthe output of the sum circuit into time domain; and a truncatorconfigured to truncate the time domain output of the sum circuit toreduce a number of taps of the IQ mismatch correction function circuitand generate the enhanced IQ mismatch correction function.
 11. The IQsignal receiver of claim 3 further comprises, a feedback circuitconfigured to feed back the enhanced IQ mismatch correction function tothe error mitigation circuit, wherein the error mitigation circuit isconfigured to determine an error of the enhanced IQ mismatch correctionfunction based on a difference between a value of the enhanced IQmismatch correction function corresponding to the at least one frequencybin and the IQ mismatch estimate corresponding to the respective bin ofthe at least one frequency bin; and the enhanced IQ mismatch correctionfunction generator is further configured to generate a subsequentenhanced IQ mismatch correction function based on the fed back enhancedIQ mismatch correction function and the error of the fed back enhancedIQ mismatch correction function.
 12. The IQ signal receiver of claim 1,wherein the correction function circuit comprising, an IQ mismatchcorrection function generator configured to generate the initial IQmismatch correction function and the enhanced IQ mismatch correctionfunction; and a feedback loop configured to determine the differencebetween the value of the initial IQ mismatch correction functioncorresponding to the at least one frequency bin and the IQ mismatchestimates corresponding to a respective bin of the at least onefrequency bin, and output the difference as error of the initial IQmismatch correction function to the IQ mismatch correction functiongenerator to generate the enhanced IQ mismatch correction function. 13.The IQ signal receiver of claim 12, wherein the IQ mismatch correctionfunction generator comprising, an interpolator configured to interpolatethe IQ mismatch estimates generated by the IQ imbalance estimationfunction circuit; an inverse fast fourier transform circuit configuredto inverse fast fourier transform the interpolated IQ mismatch estimatesgenerated by the interpolator; and a truncator configured to truncatethe inverse fast fourier transformed interpolated IQ mismatch estimatesand generate the initial IQ mismatch correction function.
 14. The IQsignal receiver of claim 13, wherein the IQ mismatch correction functiongenerator further comprising, a convergence detector coupled to theinterpolator; a sum circuit coupled to the truncator; and a delaycircuit coupled to the sum circuit, wherein the convergence detector isconfigured to determine whether values of the initial IQ mismatchcorrection function corresponding to the at least one frequency bin hasconverged with the IQ mismatch estimates corresponding to the respectivebin of the at least one frequency bin generated by the IQ imbalanceestimation function circuit based on the error output from the feedbackloop, and output at least a subset of the error; wherein theinterpolator is configured to interpolate the at least subset of theerror output from the convergence detector; wherein the inverse fastfourier transform circuit is configured to inverse fast fouriertransform the interpolated at least subset of the error output from theinterpolator; wherein the truncator is configured to truncate theinversed fast fourier transformed interpolated at least subset of theerror to reduce a number of taps of the IQ mismatch correction functioncircuit; wherein the delay circuit is configured to delay output of theinitial IQ mismatch correction function to the sum circuit; and whereinthe sum circuit is configured to generate the enhanced IQ mismatchcorrection function by adding the delayed initial IQ mismatch correctionfunction to an output from the truncator.
 15. The IQ signal receiver ofclaim 14, wherein the feedback loop is further configured to feedbackthe enhanced IQ mismatch correction function, determine errors of theenhanced IQ mismatch correction function based on a difference betweenvalues of the enhanced IQ mismatch correction function corresponding tothe at least one frequency bin and the IQ mismatch estimatescorresponding to the respective bin of the at least one frequency bins,and output the errors of the enhanced IQ mismatch correction function tothe IQ mismatch correction function generator; and the IQ mismatchcorrection function generator is further configured to generate asubsequent version of the enhanced IQ mismatch correction function basedon the error of the enhanced IQ mismatch correction function output bythe feedback loop.
 16. The IQ signal receiver of claim 15, wherein theconvergence detector is further configured to determine whether valuesof the enhance IQ mismatch correction function corresponding to the atleast one frequency bin has converged with the IQ mismatch estimatescorresponding to a the respective bin of the at least one frequency bingenerated by the IQ imbalance estimation circuit, based on the error ofthe enhanced IQ mismatch correction function output from the feedbackloop; and wherein the IQ mismatch correction function generator isconfigured to repeat generating the subsequent version of the enhancedIQ mismatch correction function until the convergence detectordetermines the feedback enhanced IQ mismatch correction function isconverged or until subsequent versions of the enhanced IQ mismatchcorrection function are generated a preset number of times, or for apreset period of time.
 17. The IQ signal receiver of claim 14, whereinthe subset of the error is zero where the values of all initial IQmismatch correction functions corresponding to all of the at least onefrequency bin converged.